College Physics

1
College Physics

• Introduction
• and
• Chapter 1

2
Physics

• Fundamental Science
• foundation of other sciences
• Divided into five major areas
• Mechanics
• Thermodynamics
• Electromagnetism
• Relativity
• Quantum Mechanics

3
Mechanics

• Has many basic principles that are used in the
  other major areas
• Based on studies of motion by Greeks through
  Galileo, Newtons Principia in 1687
• Accurately describes actions at human speed, size

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Importance of Math in Physics

• Accurate description of observations, outcomes
• Allows for prediction of results, outcomes
• Math allows for machines and products to be
  designed for precise, dangerous, and/or expensive
  operations and not created by trail and error

5
The Mars Climate Orbiter

• Crashed because of a mix-up in units of
  measurement
• Mixed up use of Metric and US units in
  design/operation

200 million dollars destroyed
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How safe would your home or car be without the
use of Math in its design?
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Measurements

• Basis of testing theories in science,
  quantitative analysis
• Need to have consistent systems of units for the
  measurements
• Uncertainties are inherent
• Need rules for dealing with the uncertainties

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Systems of Measurement

• Standardized systems
• agreed upon by some authority, usually a
  governmental body
• SI -- Systéme International
• agreed to in 1960 by an international committee
• main system used in this text
• also called mks for the first letters in the
  units of the fundamental quantities

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Other Systems of Measurements

• cgs -- Gaussian system (small things)
• named for the first letters of the units it uses
  for fundamental quantities
• US Customary
• everyday units
• often uses weight, in pounds, instead of mass as
  a fundamental quantity

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Basic Quantities and Their Dimension

• Length L
• Mass M
• Time T

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Length- how far

• Units
• SI -- meter, m
• cgs -- centimeter, cm
• US Customary -- foot, ft
• Defined in terms of a meter -- the distance
  traveled by light in a vacuum during a given time

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Mass amount of matter

• Units
• SI -- kilogram, kg
• cgs -- gram, g
• USC -- slug, slug
• Defined in terms of kilogram, based on a specific
  cylinder kept at the International Bureau of
  Standards

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Standard Kilogram
Why so many jars?
14
Time

• Units
• seconds, s in all three systems
• Defined in terms of the oscillation of radiation
  from a cesium atom

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US Official Atomic Clock
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Fig. T1.3, p.5
Slide 16
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Conversions

• When units are not consistent, you may need to
  convert (change)
• Units can be treated like algebraic quantities
  that can cancel each other out

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Metric Prefixes

• Prefixes correspond to powers of 10
• Each prefix has a specific name
• Each prefix has a specific abbreviation
• Some are used much more than others

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How to convert metric units using the chart
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Want more detail and practice?

• Look at the conversion power-point on website
• Do Practice questions on this and scientific
  notation

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Dimensional Analysis

• Technique to check the correctness of an equation
• Both sides of equation must have the same
  dimensions
• Dimensions (length, mass, time, combinations) can
  be treated as algebraic quantities
• add, subtract, multiply, divide

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Dimensional Analysis, cont.

• Works great with unit conversions (Roads Method)
• Multiply units of original value by form of one
  to change unit type, not value

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Example

• 25 km/hr into meters and seconds

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Back to Measurement

• Compare an unknown quantity to a standard

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Uncertainty in Measurements

• There is uncertainty in every measurement, this
  uncertainty carries over through the calculations
• need a technique to account for this uncertainty
• We will use rules for significant figures to
  approximate the uncertainty in results of
  calculations

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Significant Figures

• Can be clarified by using scientific notation
• A significant figure is one that is reliably
  known
• All non-zero digits are significant
• Zeros are significant when
• between other non-zero digits
• after the decimal point and another significant
  figure

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Operations with Significant Figures

• Accuracy -- number of significant figures
• When multiplying or dividing, round the result to
  the same accuracy as the least accurate
  measurement
• When adding or subtracting, round the result to
  the smallest number of decimal places of any term
  in the sum

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Examples of various units measuring a quantity
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Sig figs examples

• 1.6 , 100 , 302. 090
• 14.5 6.09
• 12.3 x 5.60

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Where sig figs play a roll in class

• Lab results
• Using the calculator results to answer questions
• Not as important in Physics compared to
  Chemistry.
• We are not usually working with small amounts of
  dangerous chemicals

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Estimate using Order of Magnitude

• Approximation based on a number of assumptions
• may need to modify assumptions if more precise
  results are needed
• Order of magnitude is the power of 10 that applies

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Measurement Lab
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Precision vs- Accuracy

• Precision
• exactness (level of value detail)
• Determine by small unit of measure
• Something measured to mm is more precise than
  things measured in cm
• Accuracy
• how close to the true value it is

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Comparing accuracy and precision to archery

• If the center represents the true value

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Accuracy and Precision in Physics

• Accuracy- percent error in a number of labs
• Precision- being careful to use appropriate
  measurements

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Physics (at this level) tends to not be very
accurate or particularly precise

• But that does not mean you slack off while
  measuring!

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How would you define

• Hypothesis
• Theory
• Law

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Difference between

• Hypothesis (frontier, speculative, educated
  guess how values relate)
• Theory (established, tested, explains
  observations, laws)
• Law (Rule of nature shown true in countless
  tests, universally recognized)

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Newtons Universal Law of Gravity

• All Objects with mass are attracted to each
  other. The force of attraction is based on the
  objects mass and how far they are apart.
• No explanation of why.

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Variables

• Dependent Factor to be tested, changes as a
  result of change in independent variable
• Independent factor changed or manipulated
  during experiment

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Coordinate Systems

• Used to describe the position of a point in space
• Coordinate system consists of
• a fixed reference point called the origin
• specific axes with scales and labels
• instructions on how to label a point relative to
  the origin and the axes

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Types of Coordinate Systems

• Cartesian
• Plane polar

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Cartesian coordinate system

• also called rectangular coordinate system
• x- and y- axes
• points are labeled (x,y)

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Plane polar coordinate system

• origin and reference line are noted
• point is distance r from the origin in the
  direction of angle ?, ccw from reference line
• points are labeled (r,?)

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Slope of a line

• Rise over run
• m ?y / ?x
• ?y difference between final y position and
  initial y position
• ?y yf - yi

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Types of Graphs

• Linear Y mx b
• Quadratic Y 3- x2
• Inverse Y 2/x
• Direct and Indirect variable relationship

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Subscripts

• Used to identify value under specific conditions
• At rest, at end, at the beginning, at a certain
  time

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Trigonometry Review
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More Trigonometry

• Pythagorean Theorem
• To find an angle, you need the inverse trig
  function
• for example,

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Where Trig is used

• When we start describing the world in more than
  one dimension.

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Problem Solving Strategy
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Problem Solving Strategy

• Read the problem
• identify type of problem, principle involved
• Draw a diagram
• include appropriate values and coordinate system
• some types of problems require very specific
  types of diagrams

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Problem Solving cont.

• Visualize the problem
• Identify information
• identify the principle involved
• list the data (given information)
• indicate the unknown (what you are looking for)

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Problem Solving, cont.

• Choose equation(s)
• based on the principle, choose an equation or set
  of equations to apply to the problem
• solve for the unknown
• Solve the equation(s)
• substitute the data into the equation
• include units

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Problem Solving, final

• Evaluate the answer
• find the numerical result
• determine the units of the result
• Check the answer
• are the units correct for the quantity being
  found?
• does the answer seem reasonable?
• check order of magnitude
• are signs appropriate and meaningful?

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Physics and Problem solving

• In a great number of problems and challenges you
  will face in this class
• The application of your knowledge is used to
  understand what the problem is talking about and
  asking for
• The rest is math

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Structure of Matter

• Matter is made up of molecules
• the smallest division that is identifiable as a
  substance
• Molecules are made up of atoms
• correspond to elements

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More structure of matter

• Atoms are made up of
• nucleus, very dense, contains
• protons, positively charged, heavy
• neutrons, no charge, about same mass a protons
• protons and neutrons are made up of quarks
• orbited by
• electrons, negatively charges, light
• fundamental particle, no structure

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Structure ofMatter